1. Field of the Invention
The current invention relates to a gas exchange valve device for an internal combustion engine, in particular of a motor vehicle, having a hydraulic apparatus, which includes a fluid circuit and at least one pressure reservoir connected to the fluid circuit and containing a piston prestressed by a device, and also includes a controllable actuating device, and having a gas exchange valve whose valve element is acted on by the actuating device.
2. Description of the Prior Art
A gas exchange valve device of the above kind is known from DE 198 26 047 A1. Such a gas exchange valve device is used when the internal combustion engine has no camshaft. An engine of this kind has the advantage that the control times for the inlet and outlet valves are independent of the position of the piston of the respective cylinder. Depending on the operating state of the engine, for example at a high speed, and depending on the torque desired by the driver, valve opening and closing times can be achieved, which permit an operation of the engine that is particularly optimized in terms of emissions and consumption.
The known hydraulic apparatus functions with a hydraulic circuit, which is supplied from a hydraulic reservoir by means of a high-pressure hydraulic pump. The actuating device has a hydraulic piston, which can be acted on in both movement directions and is connected to the valve shaft of the valve element of a gas exchange valve. By means of 2/2-on/off valves, one of the two chambers of a hydraulic cylinder can be acted on with a higher pressure, which leads to a corresponding movement of the piston and therefore of the valve element in the engine block.
The hydraulic circuit is connected to a hydraulic pressure reservoir, which is embodied as a spring-loaded piston reservoir and is used to damp oscillations in the hydraulic system. Furthermore, a similarly embodied emergency pressure reservoir is connected to one of the two chambers of the hydraulic cylinder, and in the event of a decrease of the pressure in the hydraulic line, supplies enough pressure and fluid volume so that the valve can be moved into its closed neutral position. The two pressure reservoirs function with different pressure levels, which are set by the differing rigidities of their restoring springs.
When there is a slight leakage in hydraulic circuit, if the engine to be supplied is turned off for a long period of time, then it is possible for both of the pressure reservoirs to empty out completely, which results in a complete pressure relief of the hydraulic circuit. In order to be able to keep the valve element of the gas exchange valve in the closed position even in this instance, the known gas exchange valve device is provided with an emergency closing spring, which pushes the piston of the actuating device and therefore also the valve element into the closed position in the absence of hydraulic pressure.
This assures that when the engine is restarted, the valve element does not protrude into the combustion chamber in such a way that it can collide, for example with other valve elements or even with the piston of the engine that is moving in the combustion chamber. The disadvantage of such an emergency closing spring, however, is that it is provided solely for this one special purpose and has no function otherwise. In addition, integrating the emergency closing spring into the gas exchange valve device can be problematic due to lack of available space. Finally, the emergency closing spring increases the hydraulic pressure required to open the valve element of the gas exchange valve since its closing force must also be overcome. Therefore, a higher hydraulic pressure and consequently a higher energy consumption are required in order to open the gas exchange valve during normal operation.
The object of the current invention, therefore, is to modify a gas exchange valve device of the type mentioned at the beginning in such a way that it can be produced more simply and inexpensively and can be operated with the lowest possible energy costs.
This object is attained in a gas exchange valve device of the type mentioned at the beginning in that the pressure reservoir is disposed so that in an approximately unpressurized state of the pressure reservoir, its piston at least indirectly locks the valve element of the gas exchange valve in an essentially closed position.